Cellular events originating from mechanical stress or strain are recognized to be an essential feature in biological remodeling, repair, differentiation, growth, and division, and are central to the many disease processes. Previous studies of mechanotransduction have focused on a single cell type and a single mode of mechanical stimulus and have rarely generalized from their findings to other stimuli or other cell types. Common features have been observed, however, and many mechanically inducible genes are now known. Similarly, while the postulated mechanisms of transduction are thought to have counterparts among different cell types, little is known of the extent to which the stress- sensing elements share a common physical basis or have comparable sensitivity in different cells. The broad objective of the proposed research is to identify relationships between the type of mechanical stimulus and the cellular response produced. Questions will be addressed concerning the origin (membrane or cytoskeletal), the physical mechanism (stress or strain), and the frequency-dependence of the response. Methods to be used include stimulation by optical and magnetic traps, and fluorescent visualization in single, living cells. The Specific Aims of this proposal are: Aim #1: To test the hypothesis that a threshold level exists in terms of the mechanical stimulus below which no response occurs, that this threshold value is independent of frequency, and that it differs for the mechanically-induced pathways that lead to fluctuations in calcium ion concentration [Ca2+]i, actin polymer fraction (a measure of cytoskeletal reorganization and migration), and Egr-1 gene induction. Aim #2: To test the hypothesis that the biological response of a cell is frequency dependent for a constant level of force. Aim #3: To test the hypothesis that the biological response depends on the mode and site of mechanical stimulus.